I am sure that if we were to get up, and another guy sat down in our place, Mr. Leg Spreader would suddenly figure out a way to keep his mutty thighs off of his new male CTA companion.

Would that it were so, but as a guy, I can almost promise he wouldn't. I've never really understood this phenomenon, beyond my assumption that most people are ill-mannered out of obliviousness, so I just assume it's a desire by the leg-spreader to signal to both men and women that he has enormous testicles and is or is not to be messed with, as the case may be.

For what it's worth, I don't encourage jabbing people with umbrellas, but her use of his leg as a table for her bag is perfectly appropriate, as would be stepping on his foot when exiting the bus, as a way of training barn-raised CTA passengers where their feet should be. My rule of thumb is not to go out of my way, but simply to use a politely conservative assumption of my personal space as if they weren't there.